The effects of tetrachlorobiphenyls on the electron transfer reaction of isolated rat liver mitochondria.

A comparative study was made of the effects of several symmetrical tetrachlorobiphenyls (TCBs) on the electron transfer from succinate to oxygen of rat liver mitochondria, and some differences in effects caused by the different chlorine positions of the biphenyl ring were clarified. TCBs used in this study included 2,3,2',3'-, 2,4,2',4'-, 2,5,2',5'-, 2,6,2',6'-, and 3,4,3',4'-TCBs. The inhibitory actions of 2,3,2',3'-, 2,4,2',4'-, and 2,5,2',5'-TCBs on succinate oxidase were potent, while those caused by 2,6,2',6'- and 3,4,3',4'-TCBs were significantly weak. The inhibition sites of 2,3,2',3'-, 2,4,2',4'-, and 2,5,2',5'-TCBs in succinate oxidase were succinate dehydrogenase and cytochrome b-c segment of the electron transport chain. In the cytochrome b-c segment, these TCBs acted on myxothiazol-sensitive site rather than antimycin-sensitive site. Cytochrome c oxidase was hardly affected by TCBs. These results indicate that 2,3,2',3'-, 2,4,2',4'-, and 2,5,2',5'-TCBs severely depress the electron transfer with succinate as the substrate, which secondarily reduces the synthesis of ATP. The relationship between the activity and chemical structure of TCBs is also discussed.